WO2013092079A1

WO2013092079A1 - Luminous means emitting white light

Info

Publication number: WO2013092079A1
Application number: PCT/EP2012/073190
Authority: WO
Inventors: Peter Lipowsky
Original assignee: Osram Gmbh
Priority date: 2011-12-20
Filing date: 2012-11-21
Publication date: 2013-06-27
Also published as: DE102011089144A1

Abstract

A luminous means (L1, L2) which emits white light is provided with at least one light source, in particular a semiconductor light source (6), the emission spectrum of which contains a first spectral region with a first local peak (16) and a second spectral region which is likewise provided with a local peak (17), wherein the second spectral region is at longer wavelengths than the first spectral region and includes the colour yellow, and wherein a wavelength-selective filter (10) having a transmission spectrum, which has a minimum (first transmission minimum) for increasing the general colour rendering index (Ra) in the yellow wavelength range, is situated in the beam path of the emitted light. A use of the luminous means (L1, L2) as a retrofit lamp, in particular to replace halogen lamps or incandescent lamps, is provided, in particular.

Description

description

The invention relates to a white light-emitting luminous means with at least one light source, in particular semiconductor light source whose emission spectrum contains a first spectral range with a first local peak and a second, also provided with a local peak spectral range, wherein the second spectral range at longer wavelengths lies as the first spectral range and the color includes yellow. The invention further relates to a use of such a luminous means. The illuminant is particularly suitable for the replacement of halogen lamps and incandescent bulbs, in applications that make the highest demands on the color fastness of the irradiated objects, such as in museums or dental practices.

A quality feature of artificial white light sources is their ability to render colors of irradiated bodies as unadulterated as possible to the human eye. The quality of the light is measured by the so-called general color rendering index Ra; Ra is an average of individual values Ri determined for eight specific reference colors. Black spotlights as well as natural daylight by definition have an optimum Ra value of 100.

Light sources with a "full" emission spectrum, such as incandescent or halogen lamps, also provide very high R values ^ 98. For LED light sources, where white light is obtained either by combining a blue LED with longer-wavelength emitting phosphors or by combining three in the primary colors red, green and Blue emitting LEDs, however, the Ra value is still significantly lower and is typically at 80. Warm white LED bulbs achieve slightly higher values than cool white LED spotlights.

To improve these values, considerable efforts have been made so far. Three main approaches were followed: conversion LEDs were mainly concerned with improving the spectrum of secondary radiation through new phosphor materials, modified compositions and / or the addition of other phosphors; see. on this, for example, DE 10 2004 038199 AI or US 2011/0221330 AI. In the case of multi-chip LEDs, one or more color-matched LEDs were frequently added with targeted shifting of the R, G and B spectra (compare, for example, Y. Ohno Proc. SPIE Vol.5530 (2004) p -98). The third approach was to combine both concepts as skillfully as possible, d. H. further developed phosphor mixtures with a (red) LED to combine (DE 10 2004 047789 AI). However, the improvements achieved in this way have been achieved with other disadvantages: phosphor mixtures optimized for high Ra values are relatively expensive and, in addition, lose their efficiency; when the Ra value is increased by 10 points, the luminous efficacy generally decreases by 15% to 25%. Although four or five-chip LEDs maintain relatively high efficiency, they require rather complex electronics in order to avoid color shifts due to the different temperature dependency of the various LED colors. And the mentioned compromise solution must manage with loss of brightness and increased control effort.

It is the object of the present invention to overcome the disadvantages of the prior art at least partially and In particular, to provide a white light-emitting lamp, which has a relatively high Ra value, has a high light output, requires no special control effort and last but not least can be manufactured or retrofitted at low cost.

This object is achieved by a white light-emitting lamp with at least one light source whose emission spectrum contains a first spectral range with a local intensity maximum (first peak) and a second, also provided with a local intensity maximum (second peak) spectral range, the second spectral range at is longer wavelengths than the first spectral range and includes the color yellow, wherein in the beam path of the emitted light is a wavelength-selective filter having a transmission spectrum which has a minimum (first transmission minimum) to increase the general color rendering index (Ra) in the yellow wavelength range.

This is based on the consideration that the quality of light measured with the color rendering index Ra can be improved not only by redesigning the emission spectrum, which primarily fills the spectrum, but also by selectively attenuating the emission spectrum in a wavelength-selective manner.

Such filtering can be based on spectra already existing and proven in practice light sources and can also be particularly easy to implement, such as by a suitable coating of already existing translucent (especially transparent) covers. It is preferred that the at least one light source is in the form of at least one semiconductor light source. Preferably, the at least one semiconductor light source comprises at least one light-emitting diode. If several LEDs are present, they can be lit in the same color or in different colors. A color can be monochrome (eg red, green, blue etc.) or multichrome (eg white). The light emitted by the at least one light-emitting diode can also be an infrared light (IR LED) or an ultraviolet light (UV LED). Several light emitting diodes can produce a mixed light; eg a white mixed light. The at least one light-emitting diode may contain at least one wavelength-converting phosphor (conversion LED). The phosphor may alternatively or additionally be arranged remotely from the light-emitting diode ("remote phosphor"). The at least one light-emitting diode can be in the form of at least one individually housed light-emitting diode or in the form of at least one LED chip. Several LED chips can be mounted on a common substrate ("sub-mount"). The at least one light-emitting diode can be equipped with at least one own and / or common optics for beam guidance, for example at least one Fresnel lens, collimator, and so on. Instead of or in addition to inorganic light-emitting diodes, for example based on InGaN or AlInGaP, it is generally also possible to use organic LEDs (OLEDs, for example polymer OLEDs). Alternatively, the at least one semiconductor light source may, for example, comprise at least one diode laser. It is particularly preferred if an LED light source with wavelength conversion is used as the light source. However, the type of light source is basically not limited and may include, for example, discharge lamps, incandescent lamps or fluorescent lamps. It is an embodiment that the first transmission minimum in the visible light range has an absolute minimum of the transmission spectrum.

It is still an embodiment that the first transmission minimum is between 500 nm and 600 nm, in particular between 550 nm and 600 nm.

It is still an embodiment that the transmittance of the filter in the first transmission minimum is reduced by 4% to 13%, preferably by 6% to 11% and more preferably by 7% to 10%, compared to the maximum transmittance. In other words, it is preferable that the filter has a transmittance of between 87% and 96%, preferably between 89% and 94%, and more preferably between 90% and 93% of the maximum transmittance in the above-mentioned range. Around this minimum, the transmittance can be approximately symmetrical, but it can also have a more or less pronounced asymmetry, depending on the requirements of the specific case.

Regardless of the attenuation curve of the filter, it is preferred that a relative transmittance in the entire range between 500 nm and 630 nm, in particular between 550 nm and 600 nm, by at least 1%, preferably at least 2%, is reduced or reduced.

It is a preferred embodiment for achieving a particularly good Ra improvement that the yellow attenuation is based on an emission spectrum whose first peak is between 430 nm and 465 nm, in particular between 435 nm and 460 nm, and whose second peak is between 590 nm and 630 nm nm, in particular between 595 nm and 620 nm. The second peak However, it can also be shifted towards shorter wavelengths, that is to say between approximately 530 nm and 580 nm, in particular between 545 nm and 565 nm. It is a further embodiment that the filter attenuates at least substantially only that part of the second spectral range which lies between the two peaks.

It is furthermore an embodiment that the filter also reduces the second peak by at least 2%, preferably at least 3% and particularly preferably at least 4%, of the intensity of the highest peak. It may be particularly preferred that the wavelength-selective attenuation is dimensioned such that it reduces the second peak, preferably by 2% to 6%, in particular by 3% to 5%.

It is still an embodiment that the filter also shifts the second peak to longer wavelengths, preferably by at least 3 nm, preferably by 4 nm and more preferably by at least 6 nm. The attenuation curve may in particular be such that it has a limited Displacement of the second peak toward longer wavelengths, typically by 3 nm to 8 nm, in particular by 4 nm to 8 nm, in particular by 5 nm to 7 nm causes.

It is an embodiment which supports the effect of attenuation in yellow for certain emission spectra, that the filter has a transmission maximum at shorter (typically blue) wavelengths, preferably between 380 nm and 500 nm, and more preferably between 450 nm and 500 nm , in particular a transmission maximum adjacent the first transmission minimum. The values can be further improved by means of an embodiment if the filter has a further second transmission maximum, preferably between 600 nm and 750 nm and particularly preferably between 600 nm and 650 nm. In particular, the first transmission minimum may be adjacently arranged by a further transmission maximum situated at longer (typically orange-red) wavelengths, especially between 600 nm and 750 nm and in particular between 600 nm and 650 nm, ie embedded between two transmission maxima. If then, for manufacturing reasons, for example, the transmission maxima are followed by even smaller transmission minima, the emission spectrum is attenuated only insignificantly if, as in most cases, it is only relatively weak in intensity at the wavelengths there.

It is yet another embodiment that the lighting means is provided with a transparent white light cover and that the filter is produced by a coating of the cover.

It is preferred that the cover is designed as a cover plate or as a piston, in particular of glass or plastic. In this way, even relatively high Ra values can be increased by several more points - for example with a warm white LED lamp, raising a Ra value from 88 to 92 and thus converting the lamp into the highest quality class 1A. Moreover, these quality improvements are not at the expense of individual Ri values. In fact, all of these individual values can be increased and, in addition, the values R9 to R14 provided for the reproduction of unsaturated colors (Ri with i = 9 to 14). Other important features, such as dimming or the color stability in the event of temperature fluctuations, are retained or are only minimally impaired, such as, for example, the luminous efficacy. However, the intended filter does not need to be realized on covers; rather, it may also be introduced elsewhere in the beam path of the emitted light, for example on already existing reflectors or even on the surface of the light source itself.

It is also an embodiment that the coating also antireflective. This makes it possible to dispense with a separate anti-imbalance. It is a development that at least in the yellow area, the transmission of the anti-reflective cover is reduced.

Since the wavelength-selective attenuation relates only to a relatively narrow wavelength range and moreover there is only in the range of a few percent, the inevitable loss of efficiency is inherently very low. It is reduced even further by simultaneous antireflection, especially as part of the reflected radiation finally exits the lamp due to multiple reflection. The lighting means can be used in particular as a retrofit lamp, in particular for the replacement of halogen lamps or incandescent lamps.

It is in particular an embodiment that the light source contains a blue emitting LED and at least a portion of the blue light to longer wavelengths shifting phosphor. However, the present illuminant is also suitable for white light sources of several, complementary color LEDs and even for quite different bulbs that emulate white light by color addition.

The illuminant is particularly suitable for the replacement (retro fit) of halogen lamps, light bulbs and other conventional lamps, in applications that make the highest demands on the color fastness of the irradiated objects, such as in museums or dental practices.

The invention will now be explained in more detail with reference to embodiments schematically illustrated in the figures of the drawing. Corresponding parts are provided with the same reference numerals.

1 shows a lighting means according to a first embodiment;

2 shows a luminous means according to a second embodiment;

FIG. 3 shows an emission spectrum of the luminous means according to the first exemplary embodiment, in comparison with an emission spectrum of an embodiment without

Cover plate;

Fig. 4 shows an emission spectrum of a third embodiment, compared to a version without cover; and

Fig. 5 shows an emission spectrum of a fourth embodiment, compared to an embodiment without cover.

An illustrated in Fig.l first light source LI is designed as a LED retrofit spotlight of type MR16. The Illuminant LI is about as bright as a 50W halogen bulb. It has a cooling body 2 provided with cooling fins 1, which contains a driver circuit (not shown) and below which a G05.3 socket 3 with two connection pins 4 is set. Above the heat sink 2 there is an optical system 5, which contains a circuit board 7 equipped with two 3W LEDs 6, a peripheral reflector 8 and an attached cover glass 9 made of glass. The cover 9 is internally provided with a filter in the form of a multi-layer coating 10, which is designed so that it has a non-reflective and on the other hand has a frequency-selective transmittance. How such a coating 10 can be realized is well known per se. For example, a plurality of interference layers can be matched to one another in terms of their refractive indices and thicknesses so that visible light experiences no reflection in a wide frequency and angular range. The antireflection effect of this layer structure is then to be made wavelength-selective in the desired manner, for example by means of suitable simulation programs. The cover 9 can be releasably locked in position by a retaining ring 11 which is shown in Fig.l pulled off. Fig. 2 shows a second lamp L2 in the form of an LED bulb, which is intended to replace E27 socket bulbs. It generates, with about 10W power consumption, comparable to a 75W bulb brightness. A cooling body 2 provided with cooling fins 1 of the luminous means L2 has a R27 socket 3 attached underneath. The heat sink 2, inside which in turn a (not shown) control circuit is housed, carries an optical system 5 with a board 7, on which a plurality of LED chips 6 are mounted. Of the Board 7, a glass bulb 12 is placed, which in turn is provided on the inside with a multi-layer coating 10 and frosted outside. This coating 10 is used for anti-reflection and also as a wavelength-selective filter according to the coating 10 from FIG.

3 shows the results of such a wavelength-selective antireflection coating. The graph shows along the x-axis the wavelength λ in nm and along the y-axis the light intensity I _re normalized to the main maximum, and the relative transparency T _re i of the cover (cover plate 9 or glass bulb 12).

Curve 13 represents the wavelength-dependent transmission of the coated cover 9, 12. Curve 14 shows the emission spectrum of a commercially available warm-white luminous LED light source (Cree XP-E), without cover glass. And curve 15 represents the emission spectrum of the same LED light source, this time with the coated cover 9, 12. Curve 13 reveals that the wavelength-selective transmission is reduced approximately in the range between 500 nm and 630 nm, and at most around 9% at about 580 nm. It can be seen from curve 14 that the emission spectrum of the LED light source is a first, relatively narrow emission band having a first peak 16 at about 450 nm, a relative height of about 0.6, and a half width of about 30 nm has. At longer wavelengths, there is a relatively broad emission band with a second peak 17 at about 608 nm, a half width of just under 170 nm and the normalized height of 1. Between both peaks is a local minimum 18 located at 486 nm, at which Intensity is only about 22%. Between this minimum and the second peak, the intensity curve increases, with an initial one steeper slope and flatter slope from about 528 nm to then drop to longer wavelengths after passing the apex; at about 700 nm, it again reaches the value of the local minimum.

The wavelength-selective damping of the coating 10 now has the effect that the first peak 16 remains virtually unchanged. The flatter edge of the second peak, however, is clearly saddled, with intensity losses of a maximum of about 6%. The vertex is also reduced by about 3 to 4%, with the result that the second peak 19 of the curve 15 is shifted by about 4 to 6 nm relative to the second peak 17 of the curve 14 to longer wavelengths. Fig. 4 shows the emission spectrum without coverage of a third exemplary embodiment of an LED light source on the market (Osram Oslon ™ SSL series). It differs from the spectrum of the first embodiment mainly in that the first peak 16 has a significantly lower relative intensity (about 37%) and a minimally shorter wavelength (about 440 nm). The second peak 17 is still at about 608 nm; the local minimum 18 located between the two peaks 16, 17 is more pronounced than in FIG. 3 (12% relative intensity) and also offset to shorter wavelengths (about 465 nm). In this example, the coating 10 is such that it attenuates more in the range between 500 nm and 620 nm than in the other regions of the emission spectrum, with a maximum of almost 10% at 575 nm. Accordingly, with the cover 9, 12 attached the emission spectrum shown by curve 15. The edge of the second peak 17 facing the first peak 16 is attenuated almost down to the local minimum by a maximum of at least 7%. Also the second Peak 17 has lost intensity by about 5% and at the same time is slightly broadened to longer wavelengths (peak 19). Fig. 5 shows the conditions in a likewise commercially available neutral-white emitting LED light source. This time, the strongest peak is in the blue, with the first peak 16 unchanged at 440 nm. The second peak 17 is at about 560 nm this time and has a relative intensity of just over 50%. The local minimum between both peaks is 480 nm and is particularly pronounced, with only 8% of maximum intensity. The filter (in particular the coating 10) in this example has a maximum attenuation of 10%, namely at the frequency location of the second peak 17. The attenuated region is embedded between two transmission maxima of the antireflection coating, located at 465 and 630 nm, respectively; at 695 nm there is a second, weaker transmission minimum with a transmittance of about 95%. The filter or coating 10 has the effect of reducing the second emission band symmetrically about its second peak, at most by about 5% of the normalized intensity.

Both in the third and in the fourth embodiment, the Ra values are significantly increased, once by 4 and once by 3 points. In addition, all eight individual values representing color reproduction for certain pastel shades are also improved. This also applies to values associated with unsaturated colors.

The invention is of course not limited to the illustrated embodiments. The principle of changing the emission spectrum to a higher Ra value by means of a color-selective filter in the beam path of the emitted or white light, in particular by means of a simultaneously non-reflecting multiple layer on a transparent cover 9, 12 of the light source, leaves a great deal of room for maneuver. For example, it would also be possible to use light sources which operate with emission maxima also outside the visible light, for example in the ultraviolet, or contain more than two emission maxima in the visible band; in LEDs, for example, in the combination of UV LEDs with one emitting in blue, green and red Fluorescent mixture or RGB LEDs with an amber LED.

Also, one skilled in the art is free to create the filter on substrates other than through a multiple layer, such as by suitable surface structuring.

LIST OF REFERENCE NUMBERS

1 cooling fin

2 heatsinks

3 sockets

4 pin

5 optical system

6 LEDs

7 board

8 reflector

9 cover

10 frequency-selective coating

11 retaining ring

12 glass flasks

13 wavelength-dependent transmission of a coated cover

14 Emission spectrum of a warm white LED light source

15 emission spectrum of the same warm-white LED light source with coated cover;

16 first peak of the emission spectrum with and without cover

17 second peak of the emission spectrum without cover

18 Local minimum of the emission spectrum with and without cover disc

19 second peak of the emission spectrum with cover LI bulbs

L2 bulbs

Claims

claims

White light emitting lamp (LI, L2) with at least one light source (6), in particular semiconductor light source whose emission spectrum contains a first spectral range with a first local peak (16) and a second, also provided with a local peak (17) spectral range, the second spectral range is at longer wavelengths than the first spectral range and includes the color yellow, wherein in the beam path of the emitted light is a wavelength-selective filter (10) with a transmission spectrum which (minimum) to increase the general color rendering index (Ra) in the yellow wavelength range ( first transmission minimum).

2. Lamp (LI, L2) according to claim 1, wherein the first transmission minimum of the filter (10) in the visible light range is an absolute minimum.

3. Lamp (LI, L2) according to claim 1 or 2, wherein the first transmission minimum between 500 nm and 600 nm, in particular between 550 nm and 600 nm, is located.

Illuminant (LI, L2) according to one of the preceding claims, wherein the transmittance of the filter (10) in the first transmission minimum by 4% to 13%, preferably by 6% to 11% and particularly preferably by 7% to 10%, compared to the maximum Transmittance is reduced.

Illuminant (LI, L2) according to one of the preceding claims, wherein the transmittance of the filter (10) in the entire range between 500 nm and 630 nm, in particular between 550 nm and 600 nm, by at least 1%, preferably at least 2%, from the transmission maximum.

Illuminant (LI, L2) according to one of the preceding claims, wherein the first peak (16) of the emission spectrum between 430 nm and 465 nm, in particular between 435 nm and 460 nm, and the second peak (17) of the emission spectrum between 590 nm and 630th nm, in particular between 595 nm and 620 nm, or between 530 nm and 580 nm, in particular between 545 nm and 565 nm.

Illuminant (LI, L2) according to claim 6, wherein the filter (10) mainly dampens only the part of the second spectral range which lies between the two peaks (16, 17).

Illuminant (LI, L2) according to claim 7, wherein the filter (10) also reduces the second peak (17) by at least 2%, preferably at least 3% and particularly preferably at least 4%, of the intensity of the highest peak.

Illuminant (LI, L2) according to claim 8, wherein the filter also shifts the second peak (17) to longer wavelengths, preferably by at least 4 nm and more preferably by at least 6 nm.

Illuminant (LI, L2) according to one of the preceding claims, wherein the filter (10) in the blue wavelength range has a first, preferably between 380 nm and 500 nm and more preferably between 450 nm and 500 nm, located transmission maximum.

1. Lamp (LI, L2) according to claim 10, wherein the filter (10) even in the orange-red wavelength range another, preferably between 600 nm and 750 nm and more preferably between 600 nm and 650 nm, located second transmission maximum.

2. Lamp (LI, L2) according to any one of the preceding claims, wherein the lighting means (LI, L2) with a transparent light for white light cover (9; 12), in particular a cover (9) or a piston (12) equipped and wherein the filter is produced by a coating (10) of the cover (9; 12).

3. Lamp (LI, L2) according to claim 12, wherein the coating (10) at the same time antireflective.

4. Lamp (LI, L2) according to any one of the preceding claims, wherein the light source (6) contains a blue emitting LED and at least a portion of the blue light to longer wavelengths shifting phosphor.

15. Use of a light source (LI, L2) according to one of the preceding claims as a retrofit lamp, in particular for the replacement of halogen lamps or incandescent lamps.